1 /* $OpenBSD: auth2-pubkey.c,v 1.29 2011/05/23 03:30:07 djm Exp $ */
2 /*
3 * Copyright (c) 2000 Markus Friedl. All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
15 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
16 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
17 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
18 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
19 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
20 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
21 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
23 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24 */
25
26 #include "includes.h"
27
28 #include <sys/types.h>
29 #include <sys/stat.h>
30
31 #include <fcntl.h>
32 #include <pwd.h>
33 #include <stdio.h>
34 #include <stdarg.h>
35 #include <string.h>
36 #include <time.h>
37 #include <unistd.h>
38
39 #include "xmalloc.h"
40 #include "ssh.h"
41 #include "ssh2.h"
42 #include "packet.h"
43 #include "buffer.h"
44 #include "log.h"
45 #include "servconf.h"
46 #include "compat.h"
47 #include "key.h"
48 #include "hostfile.h"
49 #include "auth.h"
50 #include "pathnames.h"
51 #include "uidswap.h"
52 #include "auth-options.h"
53 #include "canohost.h"
54 #ifdef GSSAPI
55 #include "ssh-gss.h"
56 #endif
57 #include "monitor_wrap.h"
58 #include "misc.h"
59 #include "authfile.h"
60 #include "match.h"
61
62 /* import */
63 extern ServerOptions options;
64 extern u_char *session_id2;
65 extern u_int session_id2_len;
66
67 static int
userauth_pubkey(Authctxt * authctxt)68 userauth_pubkey(Authctxt *authctxt)
69 {
70 Buffer b;
71 Key *key = NULL;
72 char *pkalg;
73 u_char *pkblob, *sig;
74 u_int alen, blen, slen;
75 int have_sig, pktype;
76 int authenticated = 0;
77
78 if (!authctxt->valid) {
79 debug2("userauth_pubkey: disabled because of invalid user");
80 return 0;
81 }
82 have_sig = packet_get_char();
83 if (datafellows & SSH_BUG_PKAUTH) {
84 debug2("userauth_pubkey: SSH_BUG_PKAUTH");
85 /* no explicit pkalg given */
86 pkblob = packet_get_string(&blen);
87 buffer_init(&b);
88 buffer_append(&b, pkblob, blen);
89 /* so we have to extract the pkalg from the pkblob */
90 pkalg = buffer_get_string(&b, &alen);
91 buffer_free(&b);
92 } else {
93 pkalg = packet_get_string(&alen);
94 pkblob = packet_get_string(&blen);
95 }
96 pktype = key_type_from_name(pkalg);
97 if (pktype == KEY_UNSPEC) {
98 /* this is perfectly legal */
99 logit("userauth_pubkey: unsupported public key algorithm: %s",
100 pkalg);
101 goto done;
102 }
103 key = key_from_blob(pkblob, blen);
104 if (key == NULL) {
105 error("userauth_pubkey: cannot decode key: %s", pkalg);
106 goto done;
107 }
108 if (key->type != pktype) {
109 error("userauth_pubkey: type mismatch for decoded key "
110 "(received %d, expected %d)", key->type, pktype);
111 goto done;
112 }
113 if (have_sig) {
114 sig = packet_get_string(&slen);
115 packet_check_eom();
116 buffer_init(&b);
117 if (datafellows & SSH_OLD_SESSIONID) {
118 buffer_append(&b, session_id2, session_id2_len);
119 } else {
120 buffer_put_string(&b, session_id2, session_id2_len);
121 }
122 /* reconstruct packet */
123 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
124 buffer_put_cstring(&b, authctxt->user);
125 buffer_put_cstring(&b,
126 datafellows & SSH_BUG_PKSERVICE ?
127 "ssh-userauth" :
128 authctxt->service);
129 if (datafellows & SSH_BUG_PKAUTH) {
130 buffer_put_char(&b, have_sig);
131 } else {
132 buffer_put_cstring(&b, "publickey");
133 buffer_put_char(&b, have_sig);
134 buffer_put_cstring(&b, pkalg);
135 }
136 buffer_put_string(&b, pkblob, blen);
137 #ifdef DEBUG_PK
138 buffer_dump(&b);
139 #endif
140 /* test for correct signature */
141 authenticated = 0;
142 if (PRIVSEP(user_key_allowed(authctxt->pw, key)) &&
143 PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
144 buffer_len(&b))) == 1)
145 authenticated = 1;
146 buffer_free(&b);
147 xfree(sig);
148 } else {
149 debug("test whether pkalg/pkblob are acceptable");
150 packet_check_eom();
151
152 /* XXX fake reply and always send PK_OK ? */
153 /*
154 * XXX this allows testing whether a user is allowed
155 * to login: if you happen to have a valid pubkey this
156 * message is sent. the message is NEVER sent at all
157 * if a user is not allowed to login. is this an
158 * issue? -markus
159 */
160 if (PRIVSEP(user_key_allowed(authctxt->pw, key))) {
161 packet_start(SSH2_MSG_USERAUTH_PK_OK);
162 packet_put_string(pkalg, alen);
163 packet_put_string(pkblob, blen);
164 packet_send();
165 packet_write_wait();
166 authctxt->postponed = 1;
167 }
168 }
169 if (authenticated != 1)
170 auth_clear_options();
171 done:
172 debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg);
173 if (key != NULL)
174 key_free(key);
175 xfree(pkalg);
176 xfree(pkblob);
177 return authenticated;
178 }
179
180 static int
match_principals_option(const char * principal_list,struct KeyCert * cert)181 match_principals_option(const char *principal_list, struct KeyCert *cert)
182 {
183 char *result;
184 u_int i;
185
186 /* XXX percent_expand() sequences for authorized_principals? */
187
188 for (i = 0; i < cert->nprincipals; i++) {
189 if ((result = match_list(cert->principals[i],
190 principal_list, NULL)) != NULL) {
191 debug3("matched principal from key options \"%.100s\"",
192 result);
193 xfree(result);
194 return 1;
195 }
196 }
197 return 0;
198 }
199
200 static int
match_principals_file(char * file,struct passwd * pw,struct KeyCert * cert)201 match_principals_file(char *file, struct passwd *pw, struct KeyCert *cert)
202 {
203 FILE *f;
204 char line[SSH_MAX_PUBKEY_BYTES], *cp, *ep, *line_opts;
205 u_long linenum = 0;
206 u_int i;
207
208 temporarily_use_uid(pw);
209 debug("trying authorized principals file %s", file);
210 if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) {
211 restore_uid();
212 return 0;
213 }
214 while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
215 /* Skip leading whitespace. */
216 for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
217 ;
218 /* Skip blank and comment lines. */
219 if ((ep = strchr(cp, '#')) != NULL)
220 *ep = '\0';
221 if (!*cp || *cp == '\n')
222 continue;
223 /* Trim trailing whitespace. */
224 ep = cp + strlen(cp) - 1;
225 while (ep > cp && (*ep == '\n' || *ep == ' ' || *ep == '\t'))
226 *ep-- = '\0';
227 /*
228 * If the line has internal whitespace then assume it has
229 * key options.
230 */
231 line_opts = NULL;
232 if ((ep = strrchr(cp, ' ')) != NULL ||
233 (ep = strrchr(cp, '\t')) != NULL) {
234 for (; *ep == ' ' || *ep == '\t'; ep++)
235 ;
236 line_opts = cp;
237 cp = ep;
238 }
239 for (i = 0; i < cert->nprincipals; i++) {
240 if (strcmp(cp, cert->principals[i]) == 0) {
241 debug3("matched principal from file \"%.100s\"",
242 cert->principals[i]);
243 if (auth_parse_options(pw, line_opts,
244 file, linenum) != 1)
245 continue;
246 fclose(f);
247 restore_uid();
248 return 1;
249 }
250 }
251 }
252 fclose(f);
253 restore_uid();
254 return 0;
255 }
256
257 /* return 1 if user allows given key */
258 static int
user_key_allowed2(struct passwd * pw,Key * key,char * file)259 user_key_allowed2(struct passwd *pw, Key *key, char *file)
260 {
261 char line[SSH_MAX_PUBKEY_BYTES];
262 const char *reason;
263 int found_key = 0;
264 FILE *f;
265 u_long linenum = 0;
266 Key *found;
267 char *fp;
268
269 /* Temporarily use the user's uid. */
270 temporarily_use_uid(pw);
271
272 debug("trying public key file %s", file);
273 f = auth_openkeyfile(file, pw, options.strict_modes);
274
275 if (!f) {
276 restore_uid();
277 return 0;
278 }
279
280 found_key = 0;
281 found = key_new(key_is_cert(key) ? KEY_UNSPEC : key->type);
282
283 while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
284 char *cp, *key_options = NULL;
285
286 auth_clear_options();
287
288 /* Skip leading whitespace, empty and comment lines. */
289 for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
290 ;
291 if (!*cp || *cp == '\n' || *cp == '#')
292 continue;
293
294 if (key_read(found, &cp) != 1) {
295 /* no key? check if there are options for this key */
296 int quoted = 0;
297 debug2("user_key_allowed: check options: '%s'", cp);
298 key_options = cp;
299 for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
300 if (*cp == '\\' && cp[1] == '"')
301 cp++; /* Skip both */
302 else if (*cp == '"')
303 quoted = !quoted;
304 }
305 /* Skip remaining whitespace. */
306 for (; *cp == ' ' || *cp == '\t'; cp++)
307 ;
308 if (key_read(found, &cp) != 1) {
309 debug2("user_key_allowed: advance: '%s'", cp);
310 /* still no key? advance to next line*/
311 continue;
312 }
313 }
314 if (key_is_cert(key)) {
315 if (!key_equal(found, key->cert->signature_key))
316 continue;
317 if (auth_parse_options(pw, key_options, file,
318 linenum) != 1)
319 continue;
320 if (!key_is_cert_authority)
321 continue;
322 fp = key_fingerprint(found, SSH_FP_MD5,
323 SSH_FP_HEX);
324 debug("matching CA found: file %s, line %lu, %s %s",
325 file, linenum, key_type(found), fp);
326 /*
327 * If the user has specified a list of principals as
328 * a key option, then prefer that list to matching
329 * their username in the certificate principals list.
330 */
331 if (authorized_principals != NULL &&
332 !match_principals_option(authorized_principals,
333 key->cert)) {
334 reason = "Certificate does not contain an "
335 "authorized principal";
336 fail_reason:
337 xfree(fp);
338 error("%s", reason);
339 auth_debug_add("%s", reason);
340 continue;
341 }
342 if (key_cert_check_authority(key, 0, 0,
343 authorized_principals == NULL ? pw->pw_name : NULL,
344 &reason) != 0)
345 goto fail_reason;
346 if (auth_cert_options(key, pw) != 0) {
347 xfree(fp);
348 continue;
349 }
350 verbose("Accepted certificate ID \"%s\" "
351 "signed by %s CA %s via %s", key->cert->key_id,
352 key_type(found), fp, file);
353 xfree(fp);
354 found_key = 1;
355 break;
356 } else if (key_equal(found, key)) {
357 if (auth_parse_options(pw, key_options, file,
358 linenum) != 1)
359 continue;
360 if (key_is_cert_authority)
361 continue;
362 found_key = 1;
363 debug("matching key found: file %s, line %lu",
364 file, linenum);
365 fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX);
366 verbose("Found matching %s key: %s",
367 key_type(found), fp);
368 xfree(fp);
369 break;
370 }
371 }
372 restore_uid();
373 fclose(f);
374 key_free(found);
375 if (!found_key)
376 debug2("key not found");
377 return found_key;
378 }
379
380 /* Authenticate a certificate key against TrustedUserCAKeys */
381 static int
user_cert_trusted_ca(struct passwd * pw,Key * key)382 user_cert_trusted_ca(struct passwd *pw, Key *key)
383 {
384 char *ca_fp, *principals_file = NULL;
385 const char *reason;
386 int ret = 0;
387
388 if (!key_is_cert(key) || options.trusted_user_ca_keys == NULL)
389 return 0;
390
391 ca_fp = key_fingerprint(key->cert->signature_key,
392 SSH_FP_MD5, SSH_FP_HEX);
393
394 if (key_in_file(key->cert->signature_key,
395 options.trusted_user_ca_keys, 1) != 1) {
396 debug2("%s: CA %s %s is not listed in %s", __func__,
397 key_type(key->cert->signature_key), ca_fp,
398 options.trusted_user_ca_keys);
399 goto out;
400 }
401 /*
402 * If AuthorizedPrincipals is in use, then compare the certificate
403 * principals against the names in that file rather than matching
404 * against the username.
405 */
406 if ((principals_file = authorized_principals_file(pw)) != NULL) {
407 if (!match_principals_file(principals_file, pw, key->cert)) {
408 reason = "Certificate does not contain an "
409 "authorized principal";
410 fail_reason:
411 error("%s", reason);
412 auth_debug_add("%s", reason);
413 goto out;
414 }
415 }
416 if (key_cert_check_authority(key, 0, 1,
417 principals_file == NULL ? pw->pw_name : NULL, &reason) != 0)
418 goto fail_reason;
419 if (auth_cert_options(key, pw) != 0)
420 goto out;
421
422 verbose("Accepted certificate ID \"%s\" signed by %s CA %s via %s",
423 key->cert->key_id, key_type(key->cert->signature_key), ca_fp,
424 options.trusted_user_ca_keys);
425 ret = 1;
426
427 out:
428 if (principals_file != NULL)
429 xfree(principals_file);
430 if (ca_fp != NULL)
431 xfree(ca_fp);
432 return ret;
433 }
434
435 /* check whether given key is in .ssh/authorized_keys* */
436 int
user_key_allowed(struct passwd * pw,Key * key)437 user_key_allowed(struct passwd *pw, Key *key)
438 {
439 u_int success, i;
440 char *file;
441
442 if (auth_key_is_revoked(key))
443 return 0;
444 if (key_is_cert(key) && auth_key_is_revoked(key->cert->signature_key))
445 return 0;
446
447 success = user_cert_trusted_ca(pw, key);
448 if (success)
449 return success;
450
451 for (i = 0; !success && i < options.num_authkeys_files; i++) {
452 file = expand_authorized_keys(
453 options.authorized_keys_files[i], pw);
454 success = user_key_allowed2(pw, key, file);
455 xfree(file);
456 }
457
458 return success;
459 }
460
461 Authmethod method_pubkey = {
462 "publickey",
463 userauth_pubkey,
464 &options.pubkey_authentication
465 };
466